package BC112_小乐乐求和;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        long num = 0;
        while (n > 0){
            num += n;
            n--;
        }
        System.out.println(num);
    }
}
